1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for transmitting an uplink signal in a wireless communication system.
2. Related Art
3rd generation partnership project (3GPP) long term evolution (LTE) evolved from a universal mobile telecommunications system (UMTS) is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) evolved from the 3GPP LTE.
As disclosed in 3GPP TS 36.211 V8.7.0 (2009-05) “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8)”, a physical channel of 3GPP LTE/LTE-A can be classified into a downlink channel, i.e., a physical downlink shared channel (PDSCH) and a physical downlink control channel (PDCCH), and an uplink channel, i.e., a physical uplink shared channel (PUSCH) and a physical uplink control channel (PUCCH).
In addition to the PUSCH and the PUCCH, a user equipment transmits various uplink signals. For example, the uplink signal may include a sounding reference signal (SRS) and a random access preamble. However, due to capability of the user equipment or a maximum transmit power limitation, there is a limitation in uplink signals that can be transmitted simultaneously. Therefore, even if a plurality of uplink signals are triggered in a specific duration, an uplink signal which satisfies a specific condition is transmitted in general.
However, since a carrier aggregation (CA) is introduced and a user equipment can receive a service provided from a plurality of serving cells, a transmission error may occur in an uplink signal between a base station and the user equipment.